Transit is a complicated topic all on its own. Yes, in Manhattan transit makes a lot of sense. The infrastructure is in place, and the population density makes automobiles actually a hindrance in a lot of ways. But something like that doesn’t spring up overnight, and many areas do not have that kind of population density, and are not layed out for efficient use of transit. To rework suburban neighborhoods for transit will take a lot more than just building train/subway lines and stations, which is complicated enough. It takes rebuilding neighborhoods to integrate schools, restaurants, shopping centers, etc in accessible manners.
But that doesn’t really invalidate your point, just explains the challenges to implementation.